Plasticization water-induced

The original proposal concerning the mode of action of auxin stated that auxin made cell walls more plastic, thus inducing a water-diffusion-pressure deficit and causing the cells to expand (7). Much evidence has since been gathered in support of this hypothesis. For example, in Avena coleoptiles it has been established that the auxin-induced increase in plasticity precedes, or coincides with, the... 

Crystallinity indexes calculated according to the method described by Segal et al. (32) showed that the old cotton has a crystallinity of about 38 . Aqueous treatments increased the crystallinity of the historic cotton sample to about 45 . However, the crystallinity of contemporary cotton, which is about 70 , was not reached (30). This increase suggests that water acts as an internal plasticizer and allows a segmental reorientation which leads to an increase in crystallinity. Water-induced crystallization of amorphous cellulose fibers has been reported (17). Kalyanaraman (33) investigated orientation factors of cotton fibers from historic samples and found that the orientation values of the museums samples are smaller than the values of present-day cottons. He opined that cotton may have lost its orientation over time. In view of this... 

The nature of the interaction between water and the polymers is important because absorbed water can adversely affect thermal, electrical and mechanical properties of the polymer. Moisture absorption increases the dielectric constant, (5.6) and dielectric loss, (7) and has been related to device reliability problems. (8) Water-induced plasticization causes hygroscopic expansion, lowering of Tg, and degradation of mechanical properties. (9)... 

Figure 2. The dipole moment of the absorbed water molecules varies from approximately 1.8 to 0.9 for the polyimides and from 1.1 to 0.7 for the polyamide-imides corresponding to fractional polarizabilities of l.O/i -0.4/x. The low values of p (<0.5p ) as seen in all the amide-imide po ymers and several of the ° polyimides, indicate restricted mobility of the water molecules. In the amide-imide polymers, we believe this is due to increased water-polymer interactions such as hydrogen bonding. Other evidence of hydrogen bonding in polyamide-imides is the water-induced plasticization and Tg lowering frequently observed.

Water-induced plasticization of polymers by disruption of intermolecular hydrogen bonding between polymer chains that are generally considered to be hydrophobic is rather common. Moy and Karasz [30] show that the lowering of Tg for an epoxy-diamine resin is proportional to the amount of water in the system. 

The structural properties of a synthetic polymer can often be modified by the service conditions to which it becomes exposed, an example being interaction with atmospheric moisture. Water induced plasticization is a common occurrence, yet depending upon the chemistry and morphology of the polymer encountered, the nature of the interaction process may take widely different routes. Some degree of specificity must be assumed in discussions relating the state of sorbed water in different polymeric systems. 

Water induces a similar phase separation at least in the bulk. It breaks the imino ether-like crosslinks specific for the DDA-cured epoxy systems in the bulk as well as in the layers on the two types of stainless steel. The proposed mechanism describes the aging behavior of DDA-cured epoxy systems well, since it explains all the observed effects of chemical modification, irreversible plasticization, and irreversible water uptake. Additionally, it is understood why there is no complete disintegration of the network the hydrolysis cleaves only the imino ether-like crosslinks but not the amine-like or the ether-like crosslinks that are also formed during curing. Hence, after hydro-thermal aging the macromolecu-lar mobility in EP2 is similar in the layers and in the bulk because the content of amine-like and ether-like crosslinks is similar. 

Min et al. [191-193] also studied water-induced melting behavior as part of their efforts to develop a plasticized melt-spinning process, and extended Frushour s work to include the effect of adding polar materials (solvents and hydrophilic polymers) and the stability of the hydrated melt at elevated temperatures. Addition of small amounts of ethylene carbonate [191] and DMF to the water further depressed both the melting and crystallization temperatures. 

Water-induced adhesion failure is quite common in a number of practical systems, ranging from electronics to environmental sensors. In microelectronics, the issue of preventing losses of adhesion is crucial in many areas of electronic packaging. As a result, any method that contributes to the understanding of factors ruling the mechanical integrity of metal-piastics interfaces (both metal-on-plastics and plastics-on-metal) deserves attention. 

An exposure of hydrophilic polymer to CO2 may result in its plasticization, which in turn increases its permeability. An increase in permeability of HMW HSPPO-13.2 films after a long-term permeation test with CO2, often referred to as CO2 conditioning, could be a result of polymer plasticization [42-44]. On the other hand, long-term permeation tests with CO2, generally did not affect permeabilities of SPPO films tested in the CV system. Therefore, if the phenomenon observed in the CP system was a result of polymer plasticization, this plasticization was induced not only by their exposure to CO2, but also by the presence of residual water in films. In any case, the above example shows another limitation of the application of a CP-type testing system in the measurement of gas permeation rates through hydrophilic films, such as SPPO. 

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